The call that froze in the lunch hour
At 12:30 the whole college is online. Students stream video. Staff join a video meeting with a parent.
The meeting freezes and the voice breaks up. The videos play fine.
How can the college make sure the meeting always works, even when the link is full?
Key words
| Word | What it means |
|---|---|
| Quality of service | rules that give some traffic a better service than other traffic |
| QoS | short for quality of service |
| Network | computers and devices joined together so they can share data |
| Packet | a small piece of data sent over a network |
| Bandwidth | the most data a link can carry each second |
| Latency | the delay for a packet to travel from one end to the other |
| Jitter | how much the delay changes from packet to packet |
| Packet loss | packets that never arrive |
| Queue | a line of packets waiting to be sent |
| Priority | how important a packet is, so how soon it is sent |
| Router | a device that passes packets between networks |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can explain how quality of service guarantees a service, and put kinds of traffic in a sensible order of priority.
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3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
What QoS does
A link is like a road. When the road is full, every car waits. A bus and a delivery van wait in the same line.
Quality of service (QoS) lets the network give some traffic a better service. It is used to guarantee a service: to promise that it will work, even when the link is busy.
How a router uses queues
A router puts packets in a queue before it sends them. Without QoS, the queue is first in, first out.
With QoS, the router first sorts packets by priority. The packet of a call goes to the front. A big download waits.
The call keeps its low latency, low jitter and low packet loss.
Kinds of traffic and what they need
| Traffic | What it needs most | Priority |
|---|---|---|
| Voice call | Low latency, low jitter, no loss | Highest |
| Video meeting | Steady bandwidth and low latency | High |
| Web and cloud apps | A fair share of bandwidth | Medium |
| It must arrive. A short delay is fine. | Low | |
| Large downloads and updates | Time is not important | Lowest |
The cells students fill in are left blank in this preview.
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3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.